Implantable cell device with supportive and radial diffusive scaffolding

ABSTRACT

The Invention features an implantable cell device that includes a membrane defining and enclosing a chamber; a distance body within the chamber for reducing the diffusion distance for a biological active factor to or across the membrane; and a support scaffold within the chamber for increasing the cell support surface area per unit volume of the chamber for distributing cells.

FIELD OF INVENTION

This present invention relates to the field of implantable medicaldevices. In particular, the invention relates to an implantable celldevice such as a capsule with supportive and diffusive scaffolding forthe treatment of diseases and disorders with encapsulated cells.

BACKGROUND OF INVENTION

Many clinical conditions, deficiencies, and disease states may beremedied or alleviated by supplying to the patient a one or morebiologically active factors produced by living cells or removing fromthe patient deleterious factors which are metabolized by living cells.In many cases, these factors may restore or compensate for theimpairment or loss of organ or tissue function. Examples of disease ordeficiency states whose etiologies include loss of secretory organ ortissue function include:

(a) diabetes, wherein the production of insulin by pancreatic islets ofLangerhans is impaired or lost;

(b) hypoparathyroidism, wherein the loss of production of parathyroidhormone causes serum calcium levels to drop, resulting in severemuscular tetany;

(c) Parkinsonism, wherein dopamine production is diminished; and

(d) anemia, which is characterized by the loss of production of redblood cells secondary to a deficiency in erythropoietin. The impairmentor loss of organ or tissue function may result in the loss of additionalmetabolic functions.

Accordingly, many investigators have attempted to reconstitute organ ortissue function by transplanting whole organs, organ tissue, or cellswhich provide secreted products or affect metabolic functions. Moreover,transplantation may provide dramatic benefits but is limited in itsapplication by the relatively small number of organs suitable andavailable for grafting. In general, the patient must be immunosuppressedin order to avert immunological rejection of the transplant, whichresults in loss of transplant function and eventual necrosis of thetransplanted tissue or cells. In many cases, the transplant must remainfunctional for a long period of time, even for the remainder of thepatient's lifetime. It is both undesirable and expensive to maintain apatient in an immunosuppressed state for a substantial period of time.

A desirable alternative to such transplantation procedures is theimplantation of cells or tissues within a physical barrier which willallow diffusion of nutrients, waste materials, and secreted products,but block the cellular and molecular effectors of immunologicalrejection. A variety of devices which protect tissues or cells producinga selected product from the immune system have been explored. Theseinclude extravascular diffusion chambers, intravascular diffusionchambers, intravascular ultrafiltration chambers, and implantation ofmicroencapsulated cells. These devices would alleviate the need tomaintain the patient in an immunosuppressed state. A problem with knowndevices is central necrosis of cells growing inside the devices. Centralnecrosis can occur after long-term implantation and give rise towidespread cell death inside the capsule.

A method and device for providing higher surface area per unit volume ofthe chamber for distributing cells and improved diffusion for deliveringappropriate quantities of needed substances, such as growth factors,neuropeptides, enzymes, hormones, or other factors or, providing otherneeded metabolic functions, for an extended period of time would be veryadvantageous to those in need of long-term treatment.

Various types of cell capsules are known. For example, U.S. Pat. No.5,786,216 discloses capsules with an inner support giving tensilestrength to the device. The support may include fins extending radiallyalong the axis of the capsule or the external surface of the innersupport may be roughened or irregularly shaped. U.S. Pat. No. 6,627,422discloses device with a mesh or yarn support for attachment of cells. WO2006/122551 discloses an encapsulated cell device having an elongatetether comprising a stiffener to make the tether more rigid.

SUMMARY OF INVENTION

According to an embodiment of the invention, an implantable cell deviceis disclosed. The device includes a membrane defining and enclosing achamber; a distance means, within the chamber, for reducing diffusiondistance for a biologically active factor to/across the membrane; and asupport means, within the chamber, for increasing cell support surfacearea per unit volume of the chamber for distributing cells.

According to another embodiment of the invention, a method formanufacturing an implantable cell device is disclosed. The methodincludes forming a chamber enclosed by a membrane, the chamber includinga distance means for reducing diffusion distance for a biologicallyactive factor to/across the membrane and a support means for increasingcell support surface area per unit volume of the chamber fordistributing cells. Thereafter, the chamber is loaded with a populationof cells, the cells being capable of secreting a biologically activefactor or providing a biological function to a recipient; and lastly,the chamber is sealed.

The device of the present invention allows for a higher long term, cellsurvival within a mammal, such as in the brain of a mammal. By long-termaccording to the present invention is intended at least 6 months, suchas at least 9 months, more preferably at least one year. Therefore, theimplanted device is useable for long-term from the time of implantation.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

The embodiments of the invention, together with its advantages, may bebest understood from the following detailed description taken inconjunction with the accompanying figures in which

FIG. 1 illustrates a cross-sectional view of the device according to anembodiment of the invention;

FIG. 2(A)-(E) illustrate the distance means according to variousembodiments of the invention;

FIG. 3(A)-(C) illustrate cross sectional front view and top view of thedistance means according to various embodiments of the invention; and

FIG. 4(A)-(E) illustrate the front view and top view of the supportmeans according to various embodiments of the invention;

FIG. 5 illustrates a distance means with a combination of varioussupport means along with a tether according to an embodiment of theinvention; and

FIG. 6 illustrates the device with dimensions of different elements ofthe device according to an embodiment of the invention.

FIG. 7 illustrates the device with a twisted wire as distance means andsupport means in the shape of bristles. Together the twisted wire andbristles define a brush scaffolding.

FIG. 8 illustrates the device wherein the distance means, here a twistedwire, protrudes through the end closure to serve as a linker to beattached to a non-illustrated tether tube.

DETAILED DESCRIPTION OF THE INVENTION

The invention is generally described with specific embodiments, such asdistance means having a circular cross section in radial direction,positioned centrally with respect to the chamber. However, the personskilled in the art would appreciate that the invention may be practisedusing alternative embodiments of this invention. Furthermore, sameelements of the device, in different figures, are identified with samenumeral.

FIG. 1 illustrates a cross-sectional view of the implantable cell deviceaccording to an embodiment of the invention. The device 100 includes amembrane 105 defining and enclosing a chamber 110, a distance means 115for reducing diffusion distance D1 for a biologically active factorto/across the membrane, and a support means 120 for increasing cellsupport surface area per unit volume of the chamber 110 for distributingcells. The distance means 115 and the support means 120 are bothpositioned within the chamber 110.

The combination of the distance means and support means results in:

a) improved, i.e. more uniform distribution of cells in the chamber,

b) reduction in the number of layers of cells in any sub-compartment ofthe chamber,

c) reduction in central necrosis, i.e. morphological changes in cellsindicative of cell death in and around central section of the chamber oraround the distance means,

d) increasing the number of viable cells within the chamber for aspecific encapsulated cell population.

Biologically Active Factor

The cells distributed within the chamber are capable of secreting abiologically active factor or providing a biological function to arecipient. The cells, in a chamber of the device, are either suspendedin a liquid medium or immobilized within a hydrogel or extracellularmatrix material. The types of cells that may be used in the presentinvention and genetic engineering of the cells for encapsulation aredescribed in WO 2006/122551, incorporated herein by reference.

The biologically active factor is selected from a group consisting ofneuropeptides, neurotransmitters, hormones, cytokines, lymphokines,enzymes, biological response modifiers, growth factors, antibodies andtrophic factors.

Membrane

The device includes the membrane 105 comprising semi permeable layer125, which defines and encloses a chamber 110. The membrane is connectedto a chamber top at one end and a chamber bottom at the other end. Themembrane includes at least one biocompatible semi-permeable layer 125across which:

-   -   the biologically active factor can pass through from the chamber        into surroundings such as a central nervous system; and    -   the nutrients can pass through from the surrounding such as a        central nervous system into the chamber.

A “biocompatible material” includes material that, after implantation ina host, does not elicit a detrimental host response sufficient to resultin the rejection of the capsule or to render it inoperable, for examplethrough degradation. In various embodiments of the invention, themembrane is made up of a material selected from a group consisting ofpolyacrylates including acrylic copolymers, polyvinylidenes, polyvinylchloride copolymers, polyurethanes, polystyrenes, polyamides, celluloseacetates, cellulose nitrates, polysulfones including polyether sulfones,polyphosphazenes, polyacrylonitriles, poly(acrylonitrile/covinylchloride), polytetrafluoroethylene, and derivatives, copolymers andmixtures thereof.

The thickness of the membrane is in the range of approximately 30-230μm. The thickness is such that the membrane provides sufficient strengthto the capsule for keeping the cells encapsulated and with this in mindbe kept as thin as possible to take up as little space as possible.

The membrane/jacket preferably has a molecular weight cutoff of lessthan 1000 kD, more preferably between 50-700 kD, more preferably between70-300 kD, more preferably between 70-150 kD, such as between 70 and 130kD. The molecular weight cutoff should be selected to ensure that thebioactive molecule may escape from the device such as a capsule whileprotecting the encapsulated cells from the immune system of the patient.

The chamber defined by the membrane may include various cross-sectionalshapes. In one embodiment, the cross-sectional shape of the chamber inthe radial direction is circular having a diameter in the range of220-1800 μm.

Diffusion Distance

The diffusion distance includes the distance covered within the chamberby the nutrient and biologically active factor, and is in the range ofapproximately 70-700 μm. The diffusion distance is defined by themaximum distance, within the chamber; a nutrient covers from an innersurface 170 of the membrane to the cells that take up the nutrient. Thediffusion distance is also defined as the maximum distance thebiologically active factor covers from cell(s) to the inner surface ofthe membrane in order to pass across the membrane into the surroundingssuch as a central nervous system.

The effective diffusion distance across the membrane is dependent on thethickness of the membrane, i.e. thickness of the semi-permeable layer125. It is comprehensible that for same thickness of the membrane,reduction in the diffusion distance to the membrane reduces theeffective diffusion distance as well.

Distance Means

The distance means 115 is placed within the chamber 110 and reduces thediffusion distance, in particular the maximal diffusion distance, for abiologically active factor to and across the membrane. The distancemeans, simultaneously reduces the maximal diffusion distance for anutrient from inner surface (refer 170, FIG. 1) of the membrane to thecell(s).

Referring now to FIGS. 2(A)-(E) illustrating the distance meansaccording to various embodiments of the invention.

In one embodiment of the invention, the distance means 115 comprises abody such as a rod, which extends longitudinally from close to a firstend (refer 175, FIG. 1) of the chamber 110 (FIGS. 2(C), (D)). In yetanother embodiment of the invention, the distance means 115 comprises abody such as a rod, which extends longitudinally from close to the firstend (refer 130, FIG. 1) of the chamber 110 to close or very close to asecond end (refer 135, FIG. 1) of the chamber 110, as illustrated inFIGS. 2(A), (B), (E).

In many embodiments, plugs will be used to close and seal one or moreends 130, 135 of the device. The plug may suitably comprise a glue. Inpreferred embodiments, the distance means is secured to one or bothplugs. The plugs may also be used to secure a tether 155 to the deviceor to secure a connection means 150, to which a tether 155 can besecured.

The glue preferably is biocompatible. In a preferred embodiment, theglue is a photo-curable glue, such as a UV curable glue, which canwithstand sterilisation with radiation, chemical sterilisation orautoclaving. Examples of UV-curable glues include urethane (meth)acrylates. These are available in different blends such as urethaneoligomer/acrylate monomer blends. Other suitable glues includecyanoacrylates and epoxy adhesives.

In another embodiment, the distance means (115 in FIG. 7) comprises abody made of a twisted wire with bristles (120 in FIG. 7) twisted intothe wire.

In another embodiment of the invention, the distance means is placedsuch that at least one end of the distance means is at a centre of thecross-section of the chamber (FIGS. 1, 2(B), (C)). In yet anotherembodiment, the ends of the distance means are off-centre to thecross-sectional centres (refer 175 & 180, FIG. 1) of the chamber 110(FIGS. 2(A), (D), (E)).

The distance means is placed at an angle to a longitudinal axis (refer140, FIG. 1) of the chamber 110 (FIGS. 1, 2(A)-(E)).

The device 100 may also include a plurality of distance means 115, asillustrated in FIGS. 2(D), (E)). The plurality of distance means areplaced within the chamber in a regular pattern (FIG. 2(E)) or anirregular pattern (FIG. 2(D)) and at least one of the plurality ofdistance means 115 comprises the support means 120.

Now referring to FIGS. 3(A)-(C), which illustrate cross sectional frontand top views of the distance means according to various embodiments ofthe invention.

The distance means includes a body such as a rod, which may includedifferent cross-sectional shapes. In one embodiment, the distance meansincludes a rod having a circular cross section. The cross-sectionaldiameter of such a rod is in the range of approximately 30-1300 μm.Typically, the ratio of the cross-sectional diameter of the distancemeans with respect to the cross-section diameter of the chamber is inthe range of 1:6 to close to 1:1.

In various embodiments of the invention, the cross-section of thedistance means includes a shape selected from a group consisting of aregular shape (FIGS. 3(A), (C)), an irregular shape (FIG. 3(B)), asymmetrical shape (FIGS. 3(A), (C)), an asymmetrical shape (FIG. 3(B))and a combination thereof.

In an embodiment of the invention, the distance means comprises atwisted rod. The twisted rod engages with the support means such as thebristles (described later), preferably by twisting. The twistinginvolves folding a length of the rod into a bent rod, usually U-shaped,with two legs. The bristles are then disposed between the two legs alonga length of the bent rod. Thereafter, the two legs of the bent rod aretwisted into each other along the length of the bent rod to form atwisted rod, such that that the bristles are secured between the legs ofthe twisted rod. The twisted rod preferably is a twisted metal wire,such as a titanium wire.

Apart from the disclosed embodiment, other options are available tosecure the bristles with the distance means such as by gluing, melting,welding, flocking etc. without altering the scope of the invention.Similar methods exist in the area of interdental brushes.

It would be appreciated by the skilled person that the diffusiondistance is defined by relative dimensions of a cross-section of thedistance means with respect to a cross-section of the chamber. Also, thediffusion distance in a particular radial direction is defined byrelative dimensions of the cross-section of the distance means withrespect to the cross-section of the chamber and positioning of thedistance means within the chamber.

The distance means is made up of a material, which is substantiallynon-toxic to cells. In various embodiments of the invention, thedistance means is made up of a material selected from a group consistingof a metal such as medical grade titanium or stainless steel, an alloysuch as medical grade titanium or stainless steel, a polymer such asincludes acrylic, polyester, polyethylene, polypropylene,polyacetonitrile, polyethylene terephthalate, nylon, polyamides,polyurethanes, polybutester, silk, cotton, chitin, carbon andbiocompatible metals and a combination thereof.

Support Means

The support means is placed within the chamber and increases cellsupport surface area per unit volume of the chamber for distributingcells. The support means increases the cell support area withoutsubstantially reducing the volume of the chamber. Therefore, increase inthe cell support area per unit volume of the chamber and maintenance ofsufficient volume of the chamber allows for having optimal population ofcells in the chamber for producing the required quantity of thebiologically active factor.

The support means, such as the plurality of plates 120′″ and alsodensely spaced bristles 120′ or plates 120″, result incompartmentalization of the chamber volume into discrete compartments(refer 165, FIG. 1), defined by sub-volume of the chamber. In otherwords, the support means 120 divides the chamber (refer 110, FIG. 1)into a plurality of compartments (refer 165, FIG. 1) definingsub-volumes within the chamber.

The compartmentalization ensures uniform distribution of cells withinthe chamber. The sub-volume may be defined by the volume of the chambersandwiched between two consecutive support means. The sub-volume mayalso be defined by the volume of the chamber around a first supportmeans until the sub-volume is intercepted by support means surroundingthe first support means.

FIG. 4(A)-(E) illustrate the front view and top view of the supportmeans according to various embodiments of the invention.

In one embodiment of the invention, according to FIG. 4(A), the supportmeans 120 comprises a plurality of bristles 120′ secured to the distancemeans 115 at at least one end 145 of the plurality of bristles 120′, theplurality of bristles 120′ being spread around and along at least a partof a length of the distance means 115.

In another embodiment, according to FIGS. 4(B) and (C), the supportmeans 120 comprises a plurality of plates (120′″ and 120″) secured tothe distance means 115, the plurality of plates (120′″ and 120″) beingspread around and along at least a part of a length of the distancemeans 115.

In the device of FIG. 4(B), the plate may be concentric and/ornon-concentric with the distance means. Furthermore, the plates 120′″may include a large plate around the distance means 115, as illustratedin FIG. 4(B) or a series of small plates 120″ spread around the distancemeans 115.

According to another embodiment of the invention, as illustrated in FIG.4(D), the support means 120 includes a plurality of filaments 120′″″with a first end of the plurality of filaments 120′″″ secured close to afirst end and a second end of the plurality of filaments 120′″″ close toa second end of the distance means 115, the plurality of filaments120′″″ being spread around and along a length of the distance means 115.In yet another embodiment of the invention, the support means 120comprises a plurality of filaments 120′″″, wherein a first end and asecond end of the plurality of the filaments 120″″ are secured to thedistance means 115 at different locations along a length of the distancemeans 115, as illustrated in FIG. 4(E). The filament is selected from agroup consisting of twisted yarns and woven mesh tubes.

The support means may include a coating of a cell-adhesive agent or cellviability enhancing substance. The support means may also include acell-adhesive agent or cell viability enhancing substance, which isco-extruded with the distance means 115.

In other embodiment of the invention, the support means may include acombination of support means 120 along and spread around the distancemeans 115, wherein the support means is selected from a group consistingof support means 120′, 120″, 120′″, 120″″, and 120′″″, as illustrated inFIG. 5.

The support means is made up of a biocompatible, substantiallynon-degradable material. The material is selected from a groupconsisting of acrylic, polyester, polyethylene, polypropylene,polyacetonitrile, polyethylene terephthalate, nylon, polyamides,polyurethanes, polybutester, silk, cotton, chitin, carbon andbiocompatible metals.

A person skilled in the art would appreciate that the support means suchas plurality of bristles and plurality of plates provide radial cellsupport between the distance means and the membrane. Therefore, incombination with the distance means, such support means not only reducesthe maximum diffusion distance but also substantially eliminates anybarrier that the nutrient may encounter while diffusing towards thedistance means or the biologically active factor may encounter whilediffusing away from the distance means. It is apparent thatsubstantially eliminating the barrier in the diffusion of the nutrientsor biologically active factor would result in improved diffusion,reduced competition among the cells for nutrients and reduced centralnecrosis.

Dimensions

FIG. 6 illustrates the device with dimensions of different elements ofthe device according to an embodiment of the invention.

The distance means 115 includes a circular cross-section in the radialdirection and has a diameter Φ1 in the range of approximately 30-1300μm. The chamber 110 includes a circular cross-section in the radialdirection and has a diameter Φ2 in the range of approximately 220-1800μm. In an embodiment, the ratio of the diameter Φ1 of the distance means115 having circular cross-section relative to the diameter Φ2 of thechamber 110 having circular cross section is in the range ofapproximately 1:6 to close to 1:1.

The diffusion distance D1 is typically in the range of approximately70-700 μm and the thickness T of the membrane 125 is in the range ofapproximately 30-230 μm.

The device 100 is typically an elongated cylindrical capsule, where thediameter Φ of the cylinder is in the range of approximately 320-2300 μmand length L of the elongated capsule is in the range of approximately3-60 mm.

Method for Manufacturing

The invention relates to a method for manufacturing the implantable celldevice 100, the method includes forming a chamber 100 enclosed by amembrane 125, the chamber comprising a distance means 115 for reducingdiffusion distance for a biologically active factor to/across themembrane 125 and a support means 120 for increasing cell support surfacearea per unit volume of the chamber 110 for distributing cells.Thereafter, loading the chamber 110 with a population of cells, thecells being capable of secreting a biologically active factor orproviding a biological function to a recipient; and sealing the chamber110.

In an embodiment, the implantable cell device is manufactured byassembling a number of components using tools designed for this purpose.Initially, all components are cleaned thoroughly to remove particulatesassociated with component manufacturing. Using a hub/fill port asstarting point, a load tube is glued to the hub to allow injected cellsto enter through the hub and load tube into the finished device. Thehollow fibre membrane is glued to the distal end of the load tube, andthe scaffold material is subsequently inserted into the hollow fibre.Alternatively, the scaffold material is inserted in the fibre beforegluing to the load tube. Finally, the end of the hollow fibre membranedistal to the load tube is closed by gluing, thereby sealing the device.Alternatively, a tether is attached to the device by means of a linkerattached to both the tether and device. In one embodiment, a cylindricaltether tube is glued to the membrane by means of a titanium linker gluedto both the tether and membrane.

Instead of using a titanium linker, the distance means 115 can be madeto protrude through the end glue seal to function as a linker forattachment of a cylindrical tether tube to the device as illustrated inFIG. 8. The assembled devices are sterilized, e.g. by autoclaving,chemical sterilisation or irradiation before cell filling.

In one embodiment, the distance means 115 is placed in the chamber 110such that the distance means 115 is secured to close to a first end 175of the chamber 110. In another embodiment, the distance means 115 isplaced in the chamber 110 such that a first end of the distance means115 is secured close to a first end 175 of the chamber 110 and a secondend of the distance means 115 is secured close to a second end 180 ofthe chamber 110. In another embodiment, the distance means 115 is madeto protrude from the first end 175 or second end 180 to function as alinker to a cylindrical tether tube. In other embodiments, the distancemeans 115 is placed such that at least one end of the distance means isat a centre of the cross-section of the chamber 110; or the ends of thedistance means 115 are off-centre to the cross-sectional centres of thechamber 110. The distance means is placed at an angle to a longitudinalaxis of the chamber.

In an embodiment, the support means 120 comprising a plurality ofbristles 120′ secured to the distance means 115 at at least one end ofthe plurality of bristles 145;

and the plurality of bristles 120′ are spread around and along at leasta part of a length of the distance means 115.

In another embodiment, the support means 120 comprising a plurality ofplates 120″/120′″ are secured to the distance means 115; and theplurality of plates 120″/120′″ are spread around and along at least apart of a length of the distance means 115.

In yet another embodiment, the support means 120 comprising a pluralityof filaments 120′″″ are secured with a first end of the plurality offilaments 120′″″ close to a first end of the distance means 115 and asecond end of the plurality of filaments 120′″″ close to a second end ofthe distance means 115; and the plurality of filaments 120′″″ are spreadaround and along a length of the distance means 115.

In yet another embodiment, the support means 120 comprising a pluralityof filaments 120″″ are secured to the distance means 115 such that afirst end and the second end of the plurality of the filaments 120″″ aresecured at different locations along a length of the distance means 115.

The support means 120 may be coated with a cell-adhesive agent or cellviability enhancing substance. In another embodiment, the support means120 comprising a cell-adhesive agent or cell viability enhancingsubstance are co-extruded with the distance means.

According to an embodiment, a plurality of distance means 115 are placedwithin the chamber 110 in a regular pattern or an irregular pattern,wherein at least one of the plurality of the distance means 115comprises the support means 120.

The device 100 may further be provided with a connecting means 150 forconnecting with a distal end 160 of an elongated tether 155.

The method includes manufacturing steps to include other features of thedevice.

OTHER EMBODIMENTS OF THE INVENTION

Implantable Means

According to FIG. 5, the device 100 includes a connecting means 150 forconnecting the device 100 with a distal end 160 of an elongated tether155.

A vehicle for positioning the cell device includes the cell device 100and the tether 155 that extends from the capsule and which is of alength sufficient to reach at least from the treatment site to theproximity of the insertion site thereby facilitating fixation of thecapsule at the insertion site, e.g. to the outer surface of the skull.The insertion site is subsequently covered by skin. In an alternativeapproach, the cannula is removed prior to the insertion of the capsuleinto the treatment site.

In an embodiment, to facilitate that the cell device may be pushed intothe treatment site by use of the tether, it may be necessary to stiffenthe tether, e.g. by locating a small diameter wire portion of the pusherinto a hollow cavity of the tether.

To ensure that the cell device is placed accurately at the treatmentsite; it is desired that when the device is being pushed into thetreatment site, the device maintains an acceptable level of resistanceagainst deformation under the compressive stress conditions of pushingsuch as when the device is subjected to a uniaxial compressive stress.When the device is being pushed, such resistance restricts significantor any deformation of the device such as restricting spreading of thedevice in a radial or lateral direction. The distance means, included inthe device, provides enough resistance against deformation such that thedevice attains an effective resistance against significant or anydeformation when the device is subjected to the compressive stress ofpushing, thereby allowing an accurate and reliable positioning of thedevice at the treatment site. It is comprehensible that for samecompressive stress condition, the effective resistance againstsignificant or any deformation of the device with the distance meansincluded therein is substantially higher than the resistance againstsuch deformation if the distance means was not included in the celldevice.

It is also desired that the device does not bend when being pushed intothe treatment site. The distance means also serves to provide the devicewith a higher degree of stiffness and resistance against bending.

Storage Container

Cell devices with or without tethers of the kind known from the priorart have been stored and shipped in storage containers of the kinddescribed in U.S. Pat. No. 5,681,740. The containers have securing meansthat secure the capsule and/or the tether to the bottom of thecontainer. The securing means serve to avoid undue contact between thedevice and other components. The securing means have a smaller diameterthan the device/tether to secure the capsule in position in severalplaces.

In an embodiment, the device comprising the cells is stored in thestorage container (not shown) having an opening into a container cavityfor storing the device immersed in a fluid medium, and a closure forclosing the opening, the closure comprising fixation means for attachingthe device to the closure.

The container may form an elongated cavity extending along thelongitudinal axis 140 for storing of the device in an elongatedoutstretched condition. Other inner shapes of the container areconceivable depending on the dimensions of the therapy system.

The closure may comprise a fixation member of a resilient material andprovided with an opening dimensioned to narrowly surround a grippedportion of the device thereby to detachably attach the device to theclosure. Preferably, the fixation member forms part of a seal providedbetween the container and the closure to facilitate antibacterialstorage of the implantable cell device. Additionally, the closure maycomprise an outer surface with fixation means for attaching a separatehandle to the closure.

Encapsulated Cell Therapy

The cell device such as a capsule, in the following referred to as thecapsule, has a membrane which is tailored to control diffusion ofmolecules, such as growth factor hormones, neurotransmitters, peptides,antibodies and complements, based on their molecular weight or size.Using encapsulation techniques, cells can be transplanted into a hostwithout immune rejection, either with or without use ofimmunosuppressive drugs. Useful biocompatible polymer capsules usuallycontain a core/chamber that contains cells, either suspended in a liquidmedium or immobilised within an immobilising matrix, and a surroundingor peripheral region of permselective matrix or membrane (“jacket”) thatdoes not contain isolated cells, that is biocompatible, and that issufficient to protect cells in the core from detrimental immunologicalattack. Encapsulation hinders elements of the immune system fromentering the capsule, thereby protecting the encapsulated cells fromimmune destruction. The semipermeable nature of the capsule membranealso permits the biologically active molecule/factor of interest toeasily diffuse from the capsule into the surrounding host tissue andallows nutrients to diffuse easily into the capsule and support theencapsulated cells. The capsule can be made from a biocompatiblematerial. A “biocompatible material” is a material that, afterimplantation in a host, does not elicit a detrimental host responsesufficient to result in the rejection of the capsule or to render itinoperable, for example through degradation. The biocompatible materialis relatively impermeable to large molecules, such as components of thehost's immune system, but is permeable to small molecules, such asinsulin, growth factors, and nutrients, while allowing metabolic wasteto be removed. A variety of biocompatible materials are suitable fordelivery of growth factors by the composition of the invention. Numerousbiocompatible materials are known, having various outer surfacemorphologies and other mechanical and structural characteristics. Thecapsules allow for the passage of metabolites, nutrients and therapeuticsubstances while minimizing the detrimental effects of the host immunesystem. Components of the biocompatible material may include asurrounding semipermeable membrane and the internal cell-supportingscaffolding/support means. Preferably, the recombinant cells are seededonto the scaffolding, which is encapsulated by the permselectivemembrane. The filamentous cell-supporting scaffold may be made from anybiocompatible material selected from the group consisting of acrylic,polyester, polyethylene, polypropylene polyacetonitrile, polyethyleneteraphthalate, nylon, polyamides, polyurethanes, polybutester, silk,cotton, chitin, carbon, or biocompatible metals. Also, bonded fibrestructures may be used for cell implantation. Biodegradable polymersinclude those comprised of poly(lactic acid) PLA, poly(lactic-coglycolicacid) PLGA, and poly(glycolic acid) PGA and their equivalents. Foamscaffolds may be used to provide surfaces onto which transplanted cellsmay adhere. Woven mesh tubes may be used as vascular grafts.Additionally, the core can be composed of an immobilizing matrix formedfrom a hydrogel, which stabilizes the position of the cells. A hydrogelis a 3-dimensional network of cross-linked hydrophilic polymers in theform of a gel, substantially composed of water.

The membrane/jacket preferably has a molecular weight cutoff of lessthan 1000 kD, more preferably between 50-700 kD, more preferably between70-300 kD, more preferably between 70-150 kD, such as between 70 and 130kD. The molecular weight cutoff should be selected to ensure that thebioactive molecule may escape from the capsule while protecting theencapsulated cells from the immune system of the patient.

Various polymers and polymer blends can be used to manufacture thesurrounding semipermeable layer includes polyacrylates (includingacrylic copolymers), polyvinylidenes, polyvinyl chloride copolymers,polyurethanes, polystyrenes, polyamides, cellulose acetates, cellulosenitrates, polysulfones (including polyether sulfones), polyphosphazenes,polyacrylonitriles, poly(acrylonitrile/covinyl chloride), as well asderivatives, copolymers, poly(acrylonitrile/covinyl chloride) (Pan-PVC)and mixtures thereof. Preferably, the surrounding semipermeable membraneis a biocompatible semipermeable hollow fibre membrane.

The capsule can be any configuration appropriate for maintainingbiological activity and providing access for delivery of the product orfunction, including for example, cylindrical, rectangular, disk-shaped,patch-shaped, ovoid, stellate, or spherical. Moreover, the capsule canbe coiled or wrapped into a mesh-like or nested structure. If thecapsule is to be retrieved after it is implanted, configurations, whichtend to lead to migration of the capsules from the site of implantation,such as spherical capsules small enough to travel in the recipienthost's blood vessels, are not preferred. Certain shapes, such asrectangles, patches, disks, cylinders, and flat sheets offer greaterstructural integrity and are preferable where retrieval is desired. Aparticularly preferred shape is cylinder-shaped as such a shape iseasily produced from hollow fibres which can be produced industrially.When macrocapsules are used, preferably at least 10³ cells areencapsulated, such as between 10³ and 10⁸ cells are encapsulated, mostpreferably 10⁴ to 10⁶ cells are encapsulated in each device. Of course,the number of cells in each capsule depends on the size of the capsule.As a rule of thumb, in a capsule with distance and support means of thisinvention, between approximately 5,000 and 50,000 cells per μl ofcapsule (volume calculated as the volume of the chamber includingdistance means and support), more preferably from 10,000 to 40,000 cellsper μL, more preferably from 20,000 to 30,000 cells per μl may beloaded. The number of cells to be loaded also depends on the size of thecells.

Dosage may be controlled by varying the dimensions (length, diameter) ofthe capsule and/or by implanting a fewer or greater number of capsules,preferably between 1 and 10 capsules per patient.

The scaffolding/support means may be coated with extracellular matrix(ECM) molecules. Suitable examples of extracellular matrix moleculesinclude, for example, collagen, laminin, and fibronectin. The surface ofthe scaffolding may also be modified by treating with plasma irradiationto impart charge to enhance adhesion of cells.

Any suitable method of sealing the capsules may be used, including theuse of polymer adhesives or crimping, knotting and heat sealing. Inaddition, any suitable “dry” sealing method may also be used, asdescribed, e.g., in U.S. Pat. No. 5,653,687, incorporated by reference.

The encapsulated cell devices are implanted according to knowntechniques. Many implantation sites are contemplated for the devices andmethods of this invention. These implantation sites include, but are notlimited to, the central nervous system, including the brain, spinal cord(see, U.S. Pat. Nos. 5,106,627, 5,156,844, and 5,554,148, incorporatedby reference), and the aqueous and vitreous humors of the eye (see WO97/34586, incorporated by reference).

Foam Scaffolds/Support Means

The foam scaffold may be formed from any suitable material that forms abiocompatible foam with an open cell or macroporous structure with anetwork of pores. An open-cell foam is a reticulate structure ofinterconnected pores. The foam scaffold provides a non-biodegradable,stable scaffold material that allows attachment of adherent cells. Amongthe polymers that are useful in forming the foam scaffolds for thedevices of this invention are thermoplastics and thermoplasticelastomers.

Some examples of thermoplastic materials useful in forming suitable foamscaffolds are: acrylic, modacrylic, polyamide, polycarbonate, polyester,polyethylene, polypropylene, polystyrene, polysulfone, polyethersulfoneand polyvinylidene fluoride. Some examples of elastomer materials usefulin forming suitable foam scaffolds are: polyamide polyester,polyethylene, polypropylene, polystyrene, polyurethane, polyvinylalcohol, polyethylene vinylacetate, and silicone.

Thermoplastic foam scaffolds made from polysulfone and polyethersulfone,and thermoplastic elastomer foam scaffolds made from polyurethane andpolyvinyl alcohol are preferred.

The foam must have some (but not necessarily all) pores of a size thatpermits cells to attach to the walls or surfaces within the pores. Thepore size, pore density and void volume of the foam scaffold may vary.The pore shape may be circular, elliptical or irregular. Because thepore shape can vary considerably, its dimensions may vary according tothe axis being measured. For the purposes of this invention, at leastsome pores in the foam should have a pore diameter of between 20-500 μm,preferably between 50-150 μm. Preferably the foregoing dimensionsrepresent the mean pore size of the foam. If non-circular, the pore mayhave variable dimensions, so long as its size is sufficient to permitadherent cells to attach to the walls or surfaces within the pore. Inone embodiment, foams are contemplated having some elliptical pores thathave a diameter of 20-500 μm along the minor axis and a diameter of upto 1500 μm along the major axis of the elliptical pores.

In addition to the foregoing cell permissive pores sizes, preferably aleast a fraction of the pores in the foam should be less than 10 μm tobe cell impermissive but still provide channels for transport ofnutrients and biologically active molecules throughout the foam.

Pore density of the foam (i.e., the number per volume of pores that canaccommodate cells, as described above) may vary between 20-90%,preferably between 50-70%.

Similarly, the void volume of the foam may vary between 20-90%,preferably between 30-70%.

The walls or surfaces of the pores may be coated with an extracellularmatrix molecule or molecules, or other suitable molecule. This coatingcan be used to facilitate adherence of the cells to the walls of thepores, to hold cells in a particular phenotype and/or to induce cellulardifferentiation.

Preferred examples of extracellular matrix molecules (ECM) that can beadhered to the surfaces within the pores of the foams include: collagen,laminin, vitronectin, polyornithine and fibronectin. Other suitable ECMmolecules include glycosaminoglycans and proteoglycans; such aschrondroitin sulfate, heparin sulfate, hyaluron, dermatan sulfate,keratin sulfate, heparan sulfate proteoglycan (HSPG) and elastin.

The ECM may be obtained by culturing cells known to deposit ECM,including cells of mesenchymal or astrocyte origin. Schwann cells can beinduced to synthesize ECM when treated with ascorbate and cAMP. See,e.g., Baron-Van Evercooren et al., “Schwann Cell Differentiation invitro: Extracellular Matrix Deposition and Interaction,” Dev. Neurosci.,8, pp. 182-96 (1986).

In addition, adhesion peptide fragments, e.g., RGD containing sequences(ArgGlyAsp), YIGSR-containing sequences (TyrIleGlySerArg), as well asIKVAV containing sequences (IleLysValAlaVal), have been found to beuseful in promoting cellular attachment. Some RGD-containing moleculesare commercially available—e.g., PepTite-2000.™ (Telios).

The foam scaffolds of this invention may also be treated with othermaterials that enhance cellular distribution within the device. Forexample, the pores of the foam may be filled with a non-permissivehydrogel that inhibits cell proliferation or migration. Suchmodification can improve attachment of adherent cells to the foamscaffold. Suitable hydrogels include anionic hydrogels (e.g., alginateor carageenan) that may repel cells due to charge. Alternately, “solid”hydrogels (e.g., agarose or polyethylene oxide) may also be used toinhibit cell proliferation by discouraging binding of extracellularmatrix molecules secreted by the cells.

Treatment of the foam scaffold with regions of a non-permissive materialallows encapsulation of two or more distinct cell populations within thedevice without having one population overgrow the other. Thusnon-permissive materials may be used within the foam scaffold tosegregate separate populations of encapsulated cells. The distinctpopulations of cells may be the same or different cell types, and mayproduce the same or different biologically active molecules. In oneembodiment, one cell population produces a substance that augments thegrowth and/or survival of the other cell population. In anotherembodiment, multiple cell types producing multiple biologically activemolecules are encapsulated. This provides the recipient with a mixtureor “cocktail” of therapeutic substances. The devices of this inventionmay be formed according to any suitable method. In one embodiment, thefoam scaffold may be pre-formed and inserted into a pre-fabricatedjacket, e.g., a hollow fibre membrane, as a discrete component.

Any suitable thermoplastic or thermoplastic elastomer foam scaffoldmaterial may be preformed for insertion into a pre-fabricated jacket. Inone embodiment we prefer polyvinyl alcohol (PVA) sponges for use as thefoam scaffold. Several PVA sponges are commercially available. Forexample, PVA foam sponges #D-3, 60 μm pore size are suitable (RippeyCorp, Kanebo). Similarly, PVA sponges are commercially available fromIvalon Inc. (San Diego, Calif.) and Hydrofera (Cleveland, Ohio). PVAsponges are water-insoluble foams formed by the reaction of aeratedPolyvinyl alcohol) solution with formaldehyde vapor as the crosslinker.The hydroxyl groups on the PVA covalently crosslink with the aldehydegroups to form the polymer network. The foams are flexible and elasticwhen wetted and semi-rigid when dried.

The filaments used to form the yarn or mesh internal scaffold are formedof any suitable biocompatible, substantially non-degradable material.Materials useful in forming yarns or woven meshes include anybiocompatible polymers that are able to be formed into fibres such as,for example, acrylic, polyester, polyethylene, polypropylene,polyacrylonitrile, polyethylene terephthalate, nylon, polyamides,polyurethanes, polybutester, or natural fibres such as cotton, silk,chitin or carbon. Any suitable thermoplastic polymer, thermoplasticelastomer, or other synthetic or natural material with fibre-formingproperties may be inserted into a pre-fabricated hollow fibre membraneor a hollow cylinder formed from a flat membrane sheet. For example,silk, PET or nylon filaments used for suture materials or in themanufacture of vascular grafts are highly conducive to this type ofapplication. In other embodiments, metal ribbon or wire may be used andwoven. Each of these filament materials has well-controlled surface andgeometric properties, may be mass produced, and have a long history ofimplant use. In certain embodiments, the filaments may be “texturized”to provide rough surfaces and “hand-holds” onto which cell projectionsmay attach. The filaments may be coated with extracellular matrixmolecules or surface-treated (e.g. plasma irradiation or NaOH or KOHetching) to enhance cellular adhesion to the filaments.

In one embodiment, the filaments, preferably organized in a non-randomunidirectional orientation, are twisted in bundles to form yarns ofvarying thickness and void volume. Void volume is defined as the spacesexisting between filaments. The void volume in the yarn should varybetween 20-95%, but is preferably between 50-95%. The preferred voidspace between the filaments is between 20-200 μm, sufficient to allowthe scaffold to be seeded with cells along the length of the yarn, andto allow the cells to attach to the filaments. The preferred diameter ofthe filaments comprising the yarn is between 5-100 μm. These filamentsshould have sufficient mechanical strength to allow twisting into abundle to comprise a yarn. The filament cross-sectional shape can vary,with circular, rectangular, elliptical, triangular, and star-shapedcross-section being preferred.

In another embodiment illustrated in FIG. 7, the filaments or yarns 120are used as bristles in a brush scaffold, for example as a twisted wirebrush 115. The twisted wire core 115 is made from a biocompatiblematerial such as implantation grade titanium. Lengths of filament oryarn 120 are distributed along a length of wire which is bent back overthe lengths of filament or yarn and twisted by rotation to fix thefilament or yarn bristles. The bristles are cut to length to obtain abrush diameter suitable for insertion into the membrane. Within themembrane 125, the twisted wire core serves to keep the bristlesseparated and fixed within the device, to strengthen the device, and toserve as a distance means to decrease the diffusion distance within thedevice. As illustrated in FIG. 8, the twisted wire core can also be madeto protrude from a device end to serve as a linker to an attachedcylindrical tether tube.

In another embodiment, the filaments or yarns are woven into a mesh. Themesh can be produced on a braider using carriers, similar to bobbins,containing monofilaments or multifilaments, which serve to feed eitherthe yarn or filaments into the mesh during weaving. The number ofcarriers is adjustable and may be wound with the same filaments or acombination of filaments with different compositions and structures. Theangle of the braid, defined by the pick count, is controlled by therotational speed of the carriers and the production speed. In oneembodiment, a mandrel is used to produce a hollow tube of mesh. Incertain embodiments, the braid is constructed as a single layer, inother embodiments it is a multi-layered structure. The tensile strengthof the braid is the linear summation of the tensile strengths of theindividual filaments.

Examples of suitable monofilaments for use in the present invention arefound in U.S. Pat. No. 6,627,422. One example is a PET yarn which iswoven into a braid. This PET braid was constructed from a 34 strand, 44denier multifilament yarn woven onto a 760 μm O. D. mandrel with a 16carrier braider at a pick count of 20 picks per inch (ppi). The PET yarnmay also be used in non-woven strands. Another example is nylonmonofilaments woven into a braid. This nylon braid was constructed froma 13 strand, 40 denier multifilament yarn woven onto a 760 μm O. D.mandrel with a 16 carrier braider at a pick count of 18 ppi. A furtherexample includes stainless steel multifilaments woven into a braid. Thisstainless steel braid was constructed from a ribbon woven onto a 900 μmO. D. mandrel with a 16 carrier braider at a pick count of 90 ppi. Thetensile strength of these PET, nylon, and stainless steel braids was2.7, 2.4, and 3.6 kg force at break, respectively.

In one embodiment, a tubular braid is constructed. In an additionalembodiment, the braid is inserted into a hollow fibre membrane. In afurther embodiment, cells are seeded onto the hollow fibre membrane. Inan additional embodiment, the cells are allowed to infiltrate the wallof the mesh tube to maximize the surface area available for cellattachment. In this embodiment, the braid serves both as a cell scaffoldmatrix and as an inner support for the device. The increase in tensilestrength for the braid-supported device is significantly higher than inalternative approaches.

It is important to note that the Figures illustrate specificapplications and embodiments of the invention, and it is not intended tolimit the scope of the present disclosure or claims to that which ispresented therein. Throughout the foregoing description, for thepurposes of explanation, numerous specific details, such as circularcross section distance means, centrally positioned distance means,support means as bristles, etc., were set forth in order to provide athorough understanding of the invention. It will be apparent, however,to one skilled in the art that the invention may be practised withoutsome of these specific details and by employing different embodiments incombination with one another. The underlying principles of the inventionmay be employed using a virtually unlimited number of differentcombinations.

Accordingly, the scope of the invention should be judged in terms of theclaims which follow.

1. An implantable cell device comprising: a membrane defining andenclosing a chamber; a distance means, within the chamber, for reducingdiffusion distance for a biologically active factor to/across themembrane; and a support means, within the chamber, for increasing cellsupport surface area per unit volume of the chamber for distributingcells.
 2. The device according to claim 1, wherein the cells are capableof secreting a biologically active factor or providing a biologicalfunction to a recipient.
 3. The device according to any of the precedingclaims, wherein the biologically active factor is selected from a groupconsisting of neuropeptides, neurotransmitters, hormones, cytokines,lymphokines, enzymes, biological response modifiers, growth factors,antibodies and trophic factors.
 4. The device according to any of thepreceding claims, wherein the membrane is connected to a chamber top atone end and a chamber bottom at the other end.
 5. The device of claim 4,wherein the ends comprise a plug.
 6. The device of claim 5, wherein theplug comprises glue.
 7. The device according to any of the precedingclaims, wherein the membrane comprises at least one biocompatiblesemi-permeable layer across which the biologically active factor ispassed through from the chamber into surroundings such as a centralnervous system.
 8. The device according to any of the preceding claims,wherein the membrane is made up of a material selected from a groupconsisting of polyacrylates including acrylic copolymers,polyvinylidenes, polyvinyl chloride copolymers, polyurethanes,polystyrenes, polyamides, cellulose acetates, cellulose nitrates,polysulfones including polyether sulfones, polyphosphazenes,polyacrylonitriles, poly(acrylonitrile/covinyl chloride),polytetrafluoroethylene, and derivatives, copolymers and mixturesthereof.
 9. The device according to any of the preceding claims, whereinthe distance means comprises a body such as a rod, which extendslongitudinally from close to a first end of the chamber.
 10. The deviceaccording to any of the preceding claims, wherein the distance meanscomprises a body such as a rod, which extends longitudinally from closeto the first end of the chamber to close to a second end of the chamber.11. The device according to any of the preceding claims, wherein thedistance means extends through one end of the chamber.
 12. The deviceaccording to any of the preceding claims, wherein the diffusion distanceis defined by relative dimensions of a cross-section of the distancemeans with respect to a cross-section of the chamber.
 13. The deviceaccording to any of the preceding claims, wherein the diffusion distancein a particular radial direction is defined by relative dimensions ofthe cross-section of the distance means with respect to thecross-section of the chamber and positioning of the distance meanswithin the chamber.
 14. The device according to any of the precedingclaims, wherein the cross-section of the distance means includes a shapeselected from a group consisting of a regular shape, an irregular shape,a symmetrical shape, an asymmetrical shape and a combination thereof.15. The device according to any of the preceding claims, wherein thedistance means is made up of a material selected from a group consistingof a metal, an alloy, a polymer and a combination thereof.
 16. Thedevice according to 15, wherein: the metal includes a medical gradetitanium or stainless steel; the alloy includes a medical grade titaniumor stainless steel; and the polymer includes acrylic, polyester,polyethylene, polypropylene, polyacetonitrile, polyethyleneterephthalate, nylon, polyamides, polyurethanes, polybutester, silk,cotton, chitin, carbon and biocompatible metals.
 17. The deviceaccording to claim 16, wherein the distance means comprises a twistedwire.
 18. The device according to any of the preceding claims, whereinthe distance means is made up of a material, which is substantiallynon-toxic to cells.
 19. The device according to any of the precedingclaims, wherein the distance means is placed such that: at least one endof the distance means is at a centre of the cross-section of thechamber; or the ends of the distance means are off-centre to thecross-sectional centres of the chamber.
 20. The device according to anyof the preceding claims, wherein the distance means is placed at anangle to a longitudinal axis of the chamber.
 21. The device according toany of the preceding claims, wherein the support means comprises aplurality of bristles secured to the distance means at at least one endof the plurality of bristles, the plurality of bristles being spreadaround and along at least a part of a length of the distance means. 22.The device according to any of the preceding claims, wherein the supportmeans comprises a plurality of bristles intertwined into a twisted wireto constitute a brush scaffold.
 23. The device according to any of thepreceding claims, wherein the support means comprises a plurality ofplates secured to the distance means, the plurality of plates beingspread around and along at least a part of a length of the distancemeans.
 24. The device according to any of the preceding claims, whereinthe support means comprises a plurality of filaments with a first end ofthe plurality of filaments secured close to a first end and a second endof the plurality of filaments close to a second end of the distancemeans, the plurality of filaments being spread around and along a lengthof the distance means.
 25. The device according to any of the precedingclaims, wherein the support means comprises a plurality of filaments,wherein a first end and a second end of the plurality of the filamentsare secured to the distance means at different locations along a lengthof the distance means.
 26. The device according to any of the claims24-25, wherein the filament is selected from a group consisting oftwisted yarns and woven mesh tubes.
 27. The device according to any ofthe preceding claims, wherein the support means comprises a coating of acell-adhesive agent or cell viability enhancing substance.
 28. Thedevice according to any of the preceding claims, wherein the supportmeans includes a cell-adhesive agent or cell viability enhancingsubstance co-extruded with the distance means.
 29. The device accordingto any of the preceding claims, wherein the support means divides thechamber into a plurality of compartments defining sub-volumes within thechamber.
 30. The device according to any of the preceding claims,wherein the support means comprises a combination of any of the featuresof claims 21-29.
 31. The device according to any of the precedingclaims, wherein the support means is made up of a biocompatible,substantially non-degradable material.
 32. The device according to anyof the preceding claims, wherein the support means is made up of amaterial selected from a group consisting of acrylic, polyester,polyethylene, polypropylene, polyacetonitrile, polyethyleneterephthalate, nylon, polyamides, polyurethanes, polybutester, silk,cotton, chitin, carbon and biocompatible metals.
 33. The deviceaccording to any of the preceding claims, further comprising a pluralityof distance means.
 34. The device according to claim 33, wherein theplurality of distance means are placed within the chamber in a regularpattern or an irregular pattern.
 35. The device according to any of theclaims 33-34, wherein at least one of the plurality of distance meanscomprises the support means.
 36. The device according to any of thepreceding claims, further comprising a connecting means for connectingthe device with a distal end of an elongated tether.
 37. The deviceaccording to any of the preceding claims, wherein ratio of diameter ofthe distance means having circular cross-section relative to diameter ofthe chamber having circular cross section is in the range ofapproximately 1:5 to close to 1:1.
 38. The device according to any ofthe preceding claims, wherein the distance means includes a circularcross-section having a diameter in the range of approximately 50-1000μm.
 39. The device according to any of the preceding claims, wherein thechamber includes a circular cross-section having a diameter in the rangeof approximately 250-1500 μm.
 40. The device according to any of thepreceding claims wherein the diffusion distance is in the range ofapproximately 100-500 μm.
 41. The device according to any of thepreceding claims, wherein thickness of the membrane is in the range ofapproximately 50-200 μm.
 42. The device according to any of thepreceding claims, wherein the device is an elongated cylindrical capsulewith a plug in each end.
 43. The device according to claim 42, whereinthe diameter of the cylinder is in the range of approximately 350-2000μm and length of the elongated capsule is in the range of approximately5-50 mm.
 44. A method for manufacturing an implantable cell device, themethod comprising: forming a chamber enclosed by a membrane, the chambercomprising a distance means for reducing diffusion distance for abiologically active factor to/across the membrane and a support meansfor increasing cell support surface area per unit volume of the chamberfor distributing cells; loading the chamber with a population of cells,the cells being capable of secreting a biologically active factor orproviding a biological function to a recipient; and sealing the chamber.45. The method according to claim 44, further comprising placing thedistance means in the chamber such that the distance means is secured toclose to a first end of the chamber.
 46. The method according to any ofthe preceding claims 44-45, further comprising placing the distancemeans in the chamber such that a first end of the distance means issecured close to a first end of the chamber and a second end of thedistance means is secured close to a second end of the chamber.
 47. Themethod according to any of the preceding claims 44-46, furthercomprising placing the distance means such that: at least one end of thedistance means is at a centre of the cross-section of the chamber; orthe ends of the distance means are off-centre to the cross-sectionalcentres of the chamber.
 48. The method according to any of the precedingclaims 44-47, further comprising placing the distance means at an angleto a longitudinal axis of the chamber.
 49. The method according to anyof the preceding claims 44-48, further comprising: securing the supportmeans comprising a plurality of bristles to the distance means at atleast one end of the plurality of bristles; and spreading the pluralityof bristles around and along at least a part of a length of the distancemeans.
 50. The method according to any of the preceding claims 44-49,further comprising: securing the support means comprising a plurality ofplates to the distance means; and spreading the plurality of platesaround and along at least a part of a length of the distance means. 51.The method according to any of the preceding claims 44-50, furthercomprising: securing the support means comprising a plurality offilaments with a first end of the plurality of filaments close to afirst end and a second end of the plurality of filaments close to asecond end of the distance means; and spreading the plurality offilaments around and along a length of the distance means.
 52. Themethod according to any of the preceding claims 44-51, furthercomprising securing the support means comprising a plurality offilaments to the distance means such that a first end and the second endof the plurality of the filaments are secured at different locationsalong a length of the distance means.
 53. The method according to any ofthe preceding claims 44-52, further comprising coating the support meanswith a cell-adhesive agent or cell viability enhancing substance. 54.The method according to any of the preceding claims 44-53, furthercomprising co-extruding the support means comprising a cell-adhesiveagent or cell viability enhancing substance co-extruded with thedistance means.
 55. The method according to any of the preceding claims44-54, further comprising placing a plurality of distance means withinthe chamber in a regular pattern or an irregular pattern, wherein atleast one of the plurality of the distance means comprises the supportmeans.
 56. The method according to any of the preceding claims 44-55,further comprising providing the device with a connecting means forconnecting with a distal end of an elongated tether.
 57. The methodaccording to claim 44-56, wherein the device includes features claimedin any of the claims 1-43.